It is common practice in building construction to provide electrical, telephone, plumbing and other service openings through barriers such as concrete floors at the time a building is constructed and finished. While some of those openings may be used initially, others are reserved for future use. The barriers, being poured or cast concrete or the like, represent good fire barriers. Thus, openings cast or drilled therethrough can reduce the integrity of the barriers and present potential fire and heat passageways. Clearly, it is important to provide a closure fitting for each such opening to thereby restore the integrity of the barrier.
One such fitting is shown in U.S. Pat. No. 4,061,344, issued Dec. 6, 1977, to Bradley et al. That fitting includes layers of elastomeric materials and intumescent materials and includes clamping bolts extending through the fitting between end plates which may also be coated with intumescent material. A disadvantage of this structure is the direct heat path through the fitting by way of the clamping bolts, which, to some degree, reduces the effectiveness of the plug and of the intumescent material therein.